'Weight loss during marathon' article - obvious conclusion

I would anticipate that Dr. Noakes would have controlled for that, since it is an obvious resulting factor, but I haven't seen the actual BJSM version of the article.

I noticed that too. If you drink at a constant rate, what you drink in 5 hours weighs more than what you drink in 3 hours. I imagine slower runners tend to sweat less too.

But don't confuse energy requirements with weight loss and fluid intake. 8.5 ounces of water and energy drink weigh the same (another confusing factor).

Maybe it's better explained in the article (BPJM), but from the "WebMD" article, it's not clear how drinking at a constant rate says anything about the optimality of drinking to thirst. Maybe there was a questionnaire that asked if you how thirsty you felt.

In any case, I think drinking to thirst has never been shown to fail (for healthy people), and the top runners of every race tend to drink far less than the recommendation from the Gatorade Sports Science Institute.